(cl--class-allparents): Fix bug#78989

(cl--class-allparents): Fix bug#78989

Give more control over ordering when linearizing the
parent graph and avoid pathological misbehavior (such as
placing `t` in the middle of the linearization instead of the
end) when we can't "do it right".

* lisp/subr.el (merge-ordered-lists): Degrade more gracefully in case
of inconsistent hierarchies and don't do it silently.

* lisp/emacs-lisp/cl-preloaded.el (cl--class-allparents): Use the local
ordering to break ties, as in the C3 algorithm.

(cherry picked from commit 7f1cae9637f9a9d4715e101eecad391748e3bd3c)